We will describe changes in the ratio of tyrosyltubulin to total tubulin and the activity of tyrosine:tubulin ligase during the differentiation of muscle, sensory, sympathetic and ciliary ganglia and during neurite formation in neuroblastoma cell lines. We will determine whether increases in tyrosine;tubulin ligase activity cause an increased turnover of the carboxyl terminal tyrosine of the alpha chain of tubulin, the net synthesis of tyrosyltubulin from tubulin or the net hydrolysis of tyrosytubulin to tubulin. We will measure tyrosyltubulin, and tyrosine;tubulin ligase during well identified stages in neurite ourgrowth including that period when sensory ganglia are maximally responsive to nerve growth factor. We will study tyrosine:tubulin ligase-nerve growth factor activates tyrosine:tubulin ligase, stimulates the mobilization of tubulin for tyrosylation and/or microtuble formation. We will determine if tyrosylation of tubulin effects polymerizabiliiy of tubulin in vitro and whether it influences the interacton of tubulin with nerve growth factor.